Semiconductor devices having wireless communication functions for transmitting and receiving data wirelessly have been put into practical use in a variety of fields. Such semiconductor devices have been expected to further expand the market as a new mode of communication information terminals. In semiconductor devices having wireless communication functions, which are put into practical use, antennas and integrated circuits formed using semiconductor elements are formed over the same substrate. Further, semiconductor devices having wireless communication functions are also referred to as wireless tags, radio frequency (RF) tags, radio frequency identification (RFID) tags, integrated circuit (IC) tags, or identification (ID) tags.
Semiconductor devices are roughly categorized into two types: active semiconductor devices and passive semiconductor devices. The former is a semiconductor device which includes a battery inside the semiconductor device and operates with the battery as a power supply source. The latter is a semiconductor device which does not include a power supply source such as a battery inside the semiconductor device and operates with a signal input from an external interrogator (also referred to as a reader, a reader/writer, or an R/W) as a power supply source.
An active wireless tag incorporates a power supply source; therefore, as compared to a passive wireless tag, a communication distance with an interrogator can be longer. However, the active wireless tag always or regularly operates (generates a signal) regardless of whether or not an answering interrogator exists, so that power consumption is larger.
A technology by which power consumption of the active wireless tag is reduced is disclosed in Patent Document 1. The active wireless tag disclosed in Patent Document 1 includes, in addition to components of the conventional active wireless tag, a second antenna receiving a signal from the outside, an electric generator generating electricity using the signal, and a voltage detection circuit to which an output voltage of the electric generator is input, and intermittent operation is controlled by the voltage detection circuit. Accordingly, power consumption can be reduced.